In wireless communication systems, both air interface encryption and end-to-end encryption play a part in providing confidentiality services. Air interface encryption is applied to information carried on the wireless link between a base radio and a communication device, whereas end-to-end encryption is applied to information exchanged between the source communication device and the final destination communication device of the information where the information may traverse multiple wireless and/or wire-line links.
Encryption requires synchronization of any encryption parameters between the transmitting device and the receiving device in order for information to be successfully decrypted. Typically, the base radio and communication device establish a relationship well before the start of communication, allowing the air interface encryption synchronization parameters to be known a priori by the receiving communication device. However, communication devices may exchange information with a large number of other communication devices, many of which are not known before the start of communication. Because of this, the receiving communication device does not know a priori the encryption synchronization parameters for end-to-end encryption.
Flexible communication systems demand that end-to-end encryption (i.e., the confidentiality service) is applied dynamically, establishing synchronization parameters whenever communication is initiated. These synchronization parameters are typically signaled in their entirety at the beginning of a transmission. These synchronization parameters are also signaled in part throughout the duration of the transmission at a very slow rate (due to limited bandwidth) to accommodate communication devices that enter the communication session after the initial signaling, a condition that is called “late-entry”. Because the encryption synchronization information is re-transmitted throughout the transmission at a rate that is typically much slower than the information it protects, this late entry condition can cause ambiguity in the receiving communication device. Thus, if the receiving communication device misses the initial transmission of encryption synchronization information, the receiving communication device is forced to either assume an encryption state, which will likely result in processing errors, or acquire the encryption synchronization information when re-transmitted throughout the transmission at the very slow rate which will result in additional delays. For example, if a receiving communication device mistakenly believes that an end-to-end encrypted call is sent unencrypted or visa-versa, objectionable noises may be generated.
Thus, there exists a need for a method for indicating and processing multiple levels of encryption.